The present invention relates to a signal processing system for converting an analog signal into a digital signal and, more particularly, to such a signal processing system which is suitable to realize a high accurate digital discrimination in a system for reproducing information from a recording medium by using a magnetoresistive head (hereinafter, referred to as an MR head). More specifically, the present invention relates to an A/D converting technique to compensate asymmetry of the upper and lower amplitudes of a waveform which can occur in a reproduction waveform into symmetry.
There is an MR head as a reproducing head of a magnetic recording apparatus. The MR head has a feature such that sensitivity is better than that of an inductive type head. However, as for the reproduction waveform of the MR head, since the flux-to-voltage conversion of the device is nonlinear, as shown in FIG. 21, distortion such that upper and lower amplitudes differ occurs in the isolated magnetic transition. Such distortion corresponds to up to about 1.5 as a ratio of the upper and lower amplitudes. Such distortion cannot be compensated even by using a linear auto equalizer disclosed in, for example, JP-A-2-150114, so that an accuracy when discriminating as a digital signal is remarkably deteriorated.
A technique to compensate nonlinearity of a reproduction waveform by an MR head is disclosed in U.S. application Ser. No. 07/796,846, the disclosure of which is incorporated herein by reference.